Process and apparatus for recovering a gas constituent by membrane separation

ABSTRACT

A process or system employing membrane separation to recover helium from a petroleum gas well. It includes pressure actuated compressing apparatus connected to the membrane separator so as to automatically compress the recovered helium.

United States Patent Franz et al. 1 Jan. 30, 1973 [541 PROCESS AND APPARATUS FOR 2.540.152 1mm Weller iii 'lo RECOVERING A GAS TI T 3.463.603 smo Frcimsct m 65/08 BY 3,266,220 8/l966 \Voerli .55/63 [75] Inventors: William F. Franz, Gardiner; Howard Hess Glenham both of Primary ExaminerCharles N. Hart Assignee Texaco Inc. New York Attorney-Thomas Whaley and Carl Reis [22] Filed: Oct. 9, 1970 [21] Appl. No.: 79,410 ABSTRACT A process or system employing membrane separation 52 use]. ..55/l6,55/68,55/158 helium from Petroleum gas well- It 511 rm. Cl. ..B0ld 59/10 ch'des Pressure actuated comprcssirg apparatus [531 Field of Search 55/16 68 I58 nected to the membrane separator s0 as to automatically compress the recovered helium.

[56] References Cited UNITED STATES PATENTS Claims, 2 Drawing Figures 3,144,3l3 8/1964 Pfefferle ..55/l6 e3 6 62 67 hwgqgggp nE vllfiY I 53 PERMEATOR 68 l I g 83 59 934 92% 5 48 52 69V 389 w 4 I B as PERMEATOR c ilk? STAGE n V REMOVAL i 0 l PERMEATOR "'lk STAGEHI Al 97 m9 PERMEATOR /76 "ll? STAGEII M77 80/ H? ||o PERMEATOR I3 VSTAGE'E WELLHEAD GAS PROCESS AND APPARATUS FOR RECOVERING A GAS CONSTITUENT BY MEMBRANE SEPARATION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention concerns membrane separation of a constituent gas. MOre specifically, it relates to the application of membrane separation to natural gas sup- 1 plies so as to recover a particular constituent, e.g. heli- 2. Description of the Prior Art Heretofore there have been developed various structures to act as membrane separators for removing a specific constituent from a mixture of gases. Such arrangements have ordinarily involved a plurality of stages for the permeation separating steps and circulation of the gases has been carried out by pumping connections. Such pumping requires considerable energy because the permeation product is only a small percentage of the total volume of gases being circulated. Also, while natural gas often contains some helium which would be a desirable product to recover, heretofore the processes for making such recovery have not been attractive from an economic or practical point of view. This is especially true in the situations where the natural gas is high in nitrogen content so as to be too lean to support combustion.

Consequently, it is an object of this invention to provide a system, or method, for recovering a desired constituent gas from a mixture where the mixture exists in substantial quantity and under considerable pressure.

SUMMARY OF THE INVENTION Briefly, the invention concerns a process for recovering a constituent from a gas mixture by using membrane separation. The process is applicable to a situation wherein there is a source of said gas mixture under pressure which may be applied to membrane separation means. Such separation means has an inlet for said gas mixture, an effluent gas outlet under pressure, and a permeation product outlet. The process comprises a step of applying said effluent gas pressure to compress said permeation product for recovery thereof.

Again, briefly, the invention concerns a system for recovering a constituent gas from a mixture under pressure wherein said constituent is a small percentage of said mixture. The system comprises a source of said mixture under pressure, and membrane means for separating said constituent at a reduced pressure. The membrane has an inlet for said mixture and an effluent gas outlet under pressure, as well as permeation product outlet. The system also comprises pressure transfer means having an expander section connected mechanically to a compressor section as well as means for connecting said source to said membrane means inlet. The system additionally comprises means for connecting said effluent gas outlet to said expander section and means for connecting said permeation product outlet to said compressor section.

Once more, the invention may be described as a system for recovering helium from a natural gas well having a supply of petroleum gas under pressure. The system comprises in combination membrane means for separating said helium. Such means has an inlet for said petroleum gas, an effluent gas outlet and an outlet for the permeation product from said membrane. The system also comprises means for removing carbon dioxide gas from said petroleum gas, and means for connecting said supply of petroleum gas to said CO removing means. The system additionally comprises pressure actuated means for compressing said permeation product. This pressure means has an input expansion side and an output compression side. The system also comprises means for connecting said supply of petroleum gas and said CO removing means to said input side of the said pressure means. Also, the system comprises a storage tank for said helium and first means for connecting said permeation product outlet to said compression side as well as second means for connecting said compression side to said storage tank for storing the recovered helium.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects and benefits of the invention will be more fully set forth below in connection with the best mode contemplated by the inventors of carrying out the invention, and in connection with which there are illustrations provided in the drawings, wherein:

FIG. 1 is a schematic diagram illustrating a simplified system according to the invention; and

FIG. 2 is a block diagram schematically illustrating a plural stage separation means along with a C0 removal unit, all for carrying out the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 1, it is pointed out that a typical application of the invention relates to the recovery of helium from petroleum gas that is available under natural pressure. Thus, there is illustrated a well head 11 at the top of a well that contains natural gas under pressure. From the well head 11 petroleum gas is piped over a connecting line 12 to a membrane means 13 for separating helium from the gas mixture. It will be appreciated that such a separating device is known per se. However, in a combination according to this invention it is used with a supply of natural gas under pressure which permits the system to provide a continuous and unattended recovery of a desired constituent gas, e.g. helium, by merely making use of the energy from the natural gas pressure.

The so-called membrane means 13 may take various forms and is sometimes known as a permeator, since the separation of a desired constituent gas is affected by a process of permeating such gas through a membrane for separation from the gas mixture. Thus, the membrane means or permeator 13 has an inlet 16 for the petroleum gas from line 12, and an outlet 17 for effluent gas from a high pressure side 18 of the permeator 13. On the other side of a dividing wall, or membrane, 21 there is a low pressure chamber 22 that will contain the permeation product i.e. helium gas in this case, which has permeated through the membrane 21. There is another outlet 23 that has a connecting line 26 leading therefrom to an output or compression side 27 of a pressure actuated means 28.

It will be observed that there is a connecting line 31 that leads from the outlet 17 to an expansion side 32 of the means 28. Also, there is a connecting line 33 that leads from the expansion side 32 to a pipe line or the like as indicated by the caption To Pipeline.

Another connection from the compression side 27 of the pressure actuated means 28, leads out through a connecting line 36 to input connections of a plurality of pressure tanks 37.

It will be noted that with a combination of elements such as those illustrated schematically in FIG. 1, it is possible to provide for recovery of a valuable constituent, e.g. helium, from the mixture of gases that are taken from a natural petroleum well. Furthermore, such recovery may be unattended, and it is feasible for use under circumstances where the petroleum gases are too lean for converting the energy therein by means of combustion.

Referring to FIG. 2, it will be appreciated that a practical permeation type separator involves a plurality of stages for obtaining a desirably purified constituent or permeation product. Furthermore, in accordance with the invention a pressure intensifier or pressure recovery device may be employed in making use of the energy from natural pressure existing on the petroleum gases as they are found, prior to the emergence from a well.

The particular form of a separator and likewise of a pressure recovery device is not part, per se, of the invention. However, in determining the practical feasibility, it has been found that a plural stage separator along with plural transfers mechanically of the pressure energy by expansion, to pumping energy for circulation or compression at various stages, could be employed. It will be understood that the volume of petroleum gases is relatively unlimited for the purposes of this operation and the pressure at the source will remain at some adequate level.

After the last stage, it is desirable to compress the recovered constituent gas. This may be accomplished because of the relatively small volume of constituent gas, and the pressure may even be increased.

An idealized system with five separation stages as well as a so-called helium recovery stage, is illustrated in FIG. 2. This system is for recovering helium from natural gas. It will be observed that there is a line 41 with the caption Wellhead Gas applied. This brings well head gas into an expansion element 42 which actuates a compression element 43 to make a final compression of the recovered helium gas before it is delivered through a line 44.

The system between the inlet line 41 and the outlet line 44 for the recovered helium, is schematically shown, but it will be described with relation to an example that provides the results of calculations to confirm the feasibility of the system. Prior to describing that example, elements of the illustrated system will be referred to as the flow of gases through the system is traced.

Thus, the well head gases leaving expansion element 42 travel over a line 47 which leads into an expansion element 48. This element 48 is mechanically connected (as indicated by the dashed line) to a compression element 49 which acts further along in the system, as will be described more fully below.

The well head gases continue on from expansion element 48 through a line 52 to another expansion element 53. Then after these pressure drops, the gases go through a line 54 to the input side of a CO, remover 55.

It will be understood that the removal of CO may be accomplished with various known arrangements. This step is necessary for the proper operation of the permeators. The principle involved is that of scrubbing a C0 containing gas with an alkaline solution. Commonly used materials are aqueous carbonate-bicarbonate of either sodium or potassium, or aqueous solutions of either mono-, di, or triethanolamine.

After removal of the carbon dioxide from the petroleum gas mixture with a small pressure drop, the gases continue through a line 58 to an input side of a first permeator stage 59 of the helium separation system. The effluent gases, still under pressure, travel through a line 62 to a compressor section 63 and then through a line 64 to an input of helium recovery permeator 67. The effluent gases still under considerable pressure continue to flow from the output of the permeator through a line 68 to another expander element 69. Then they continue on via a line 70 to another expander element 71. Thereafter, they continue through a line 74 to expander element 75 and then through a line 76 to a final expander element 77. The output effluent gases continue through a line 80 that may be connected for any desired disposition, e.g. to a pipe line as is indicated by the caption in FIG. I.

The permeation product output from the first stage 59 travels through a line 83 to the input of the compressor element 49 which has its output connected through a line 84 to the inlet ofa second stage 85 of the separator system. The effluent gas outlet from this stage 85 is circulated back through a line 88 which connects into a line 89 coming from the permeator 67. These two lines join and feed into a compressor element'92 that has its output connected through a line 93 into the input of the first stage 59 by joining the line 58.

It may be noted that where two streams such as those just described, exist at different pressures and are combined and raised to a higher pressure, the connections (not shown) would be such that the lower pressure stream would enter the first stage of the compressor (e.g. compressor 92) while the higher pressure stream would enter a higher compression stage where interstage pressure matches such higher pressure. This is true throughout the system, wherever applicable, even though the flow diagram (FIG. 2) merely shows a joinder of the two streams.

The permeation product output from the second stage 85 flows through a line 96 to another compressor element 97 that has its outlet connected to the input of a third stage permeator 98. The effluent gas output from stage 98 is recirculated back through a line 101 to join the line 83 both of which are connected to the input of the compressor element 49 that feeds the input to the second stage permeator 85.

Permeation product output from the third stage 98 goes through a line 104 to the input of a compressor element 105. The output of this compressor feeds into a fourth permeator stage 106, and the effluent gas outlet goes to join the permeation product from the second stage permeator at the input of the compressor element 97, through a line 109.

Finally, the permeation product from the fourth stage 106 goes through a line 110 to a compressor element 113 the output from which goes to the input of a fifth and last stage 114. The effluent gas outlet from stage 114 recirculates back through a line 1 l7 and joins the permeation product in line 104 to return into the previous stage 106 via the compressor element 105. Permeation product outlet from the final stage 114 goes to the input of the compressor element 43 through comprising in combination a line 118. This compressor element delivers the pu- 5 b. an effluent gas outlet, and rified helium through the line 44. c. an outlet for the permeation product from said It is contemplated that this invention should provide membrane, an economical way of recovering helium from natural 2, me n for removing arbon dio ide from id gas that contains from 1 to 8 percent helium. An exampetroleum gas, ple 0f the operating conditions for a system as iliUS- 1o 3, means for connecting said supply of petroleum gas trated and described above with regard to FIG. 2, to said CO removing means (2) shows an overall operation that separates 99.995 per- 4. pressure actuated means for compressing said percent pure helium from 1.28 MM SCF/day of a gas that ti od t ha in is available at the wellhead at 2,240 pounds per square 1, an in ut expansion side, and inch gage pressure. The gas mixture contains 6.2 pere an output compression side, cent by volume of helium, 53.7 percent by volume of 5 means fo onne ting aid u ly of tr l m gas nitrogen, 22.0 percent by volume Of CO2, and 14.0 perand said CC)2 removing means to said input side cent by volume of methane plus 4.1 percent by volume 1) of id pressure mean (4), of other hydrocarbons. 6. a storage tank for said helium, and

In the example, the wellhead gas is expa e from 7. first means for connecting said outlet (0) to said the 2,240 p.s.i.g. to about 600 p.s.i.g. permeation prescompression id (e), and sure and the available energy is used to compress the 3 nd mean for connecting said compression helium that iS produced to 2,480 p.s.i.g. f0! storage ide (e) to said storage tank (6) for storing the and/or distribution. In addition, the wellhead pressure r overed helium, energy is used to compress two of the largest internal 2 A System according to l i 1 h i id circulation streams of the system. The additional combrane means l comprises a plurality of stages, and pression work required to recompress th l Pressure means for interconnecting said stages to recirculate helium permeation product to the succeeding stage said permeation products and said effluent gases inlet pressures and to supply the pressure drop through after the initial stages. the later permeator stages is obtained from the helium 3, A system according to claim 2 wherein there are denuded off gas (effluent from the permeator 67) that six stages with two initial stages. is available at about 400 p.s.i.g. I 4. A system for recovering helium from a mixture The examples shows flows expressed in Standard under pressure wherein said helium is a small percentcubic feet per minute (SCFM), pressures expressed in age of said mixture, comprising in combination pounds per square inch gage (p.s.i.g.) and the gas quana natural-gas well source of said mixture under prestities expressed in percent by volume. It identifies the sure, streams by number which correspond with the flow line membrane means for separating said constituent at a illustrated in FIG. 2. It will be understood that although reduced pressure having a plurality of stages for inthe compression energy balance was calculated assumcreasing the concentration of helium and each ing reversible adiabatic compression and expansion, stage having an inlet for said mixture and an efwith no allowance made for mechanical efficiency, the fluent gas outlet under pressure and a permeation calculations indicated that in this case there would be product outlet, excess pressure energy available to compensate for irrpressure transfer means having an expander section eversibilities. connected mechanically to a compressor section,

Input Stream number 41 47 52 54 58 120 59 62 64 68 70 Flow, s.c.f.m 889 889 889 889 694.4 824.5 695.9 695.0 637.2 637,2 Pressure, p.s.i.g. 2, 240 1,835 909 040 600 000 384 000 402 288 N2, CH4, etc.,vo. 93.8 93.8 93.8 93.8 92.1 91.8 99.5 99.5 100.0 100.0 H v01. percent 6.2 6.2 6.2 6.2 7.95 8.2 0.5 0.5 0.025 0.025

Input Stream number 74 76 80 89 83 84 88 96 to 98 101 Flow, s.c.f.m-. 1. 037.2 037.2 037.2 58.7 128.0 138.8 71.4 07.3 75.3 10,2 Pressure, p.s.i.g 194 141 99 5 5 600 270 5 400 355 N2, CH4, etc., v01. percent.. 100.0 100.0 100.0 04.5 50.0 48.4 90.0 4.4 4.0 2.0 H vol. percent 0.025 0.025 0.025 5.5 50.0 51.6 10.0 95.6 96.0 97.1

Input Input Stream number 104 109 to 106 110 to 114 117 118 44 Flow, s.o.f.m- 05.1 8.0 79.4 71.4 71.4 14.3 57.2 57.2 Pressure, p.s.i.g 5 352 400 5 400 336 5 2,480 N1, 0114, ctc., v01. percent 0.1 0.75 0. 1 0.0 0.0 0.0 0.0 0 H... vol. percent 99.9 99.25 99.91 99.983 99.983 99.937 99.905 99.995

The foregoing description of the invention has been means for connecting said source to said membrane made in considerable detail in accordance with the apmeans inlet, plicable statutes. However, this is not to be taken as in means for connecting said effluent gas outlet to said any way limiting the invention but merely as being 65 expander section,

descriptive thereof.

We claim: y l. A system for recovering helium from a natural gas well having a supply of petroleum gas under pressure,

means for connecting said permeation product outlet to said compressor section,

storage means for said permeation product,

means for connecting said compressor section to said storage means, and gas mixture, an effluent gas outlet under pressure and a means 'for removing carbon dioxide from said mixpermeation product outlet, comprising the steps of ture prior to introduction into said membrane applying merely said effluent gas pressure to commcan press said permeation product for recovery 5. Process for recovering helium from a petroleum th r f and gas mixture by membrane separation wherein the source of natural gas mixture under pressure is a well the gas from which is applied to membrane separation means, said separation means having an inlet for said removing carbon dioxide from said source prior to applying said gas mixture to said separation means. 

1. A system for recovering helium from a natural gas well having a supply of petroleum gas under pressure, comprising in combination
 1. membrane means for separating said helium having a. an inlet for said petroleum gas, b. an effluent gas outlet, and c. an outlet for the permeation product from said membrane,
 2. means for removing carbon dioxide from said petroleum gas,
 2. A system according to claim 1 wherein said membrane means (1) comprises a plurality of stages, and means for interconnecting said stages to recirculate said permeation products and said effluent gases after the initial stages.
 3. A system according to claim 2 wherein there are six stages with two initial stages.
 3. means for connecting said supply of petroleum gas to said CO2 removing means (2)
 4. pressure actuated means for compressing said permeation product having d. an input expansion side, and e. an output compression side,
 4. A system for recovering helium from a mixture under pressure wherein said helium is a small percentage of said mixture, comprising in combination a natural-gas well source of said mixture under pressure, membrane means for separating said constituent at a reduced pressure having a plurality of stages for increasing the concentration of helium and each stage having an inlet for said mixture and an effluent gas outlet under pressure and a permeation product outlet, pressure transfer means having an expander section connected mechanically to a compressor section, means for connecting said source to said membrane means inlet, means for connecting said effluent gas outlet to said expander section, means for connecting said permeation product outlet to said compressor section, storage means for said permeation product, means for connecting said compressor section to said storage means, and means for removing carbon dioxide from said mixture prior to introduction into said membrane means inlet.
 6. a storage tank for said helium, and
 7. first means for connecting said outlet (c) to said compression side (e), and
 8. second means for connecting said compression side (e) to said storage tank (6) for storing the recovered helium. 